1. Field of the Invention
The present invention relates to a cylindrical secondary battery, more particularly, to a cylindrical secondary battery to ensure safety when pressure is applied to the battery by an external impact.
2. Description of the Related Art
Generally, a cylindrical lithium ion secondary electrode includes an electrode assembly that is wound in an approximately cylindrical shape, a cylindrically-shaped can coupled to the electrode assembly, an electrolyte injected into an inner side of the can to transport the lithium ions, and a cap assembly coupled to one side of the can to prevent leakage of the electrolyte and disengagement of the electrode assembly.
Since such cylindrical lithium ion secondary electrodes generally have a capacity of 2000˜2400 mA, they are mainly used for notebook computers, digital cameras and camcorders, and the like, which need high-capacity power.
In one example, one such cylindrical lithium ion secondary electrode is connected in serial-parallel because the electrode requires many cells and is assembled in a hard pack of predetermined shape to be coupled to an electronic device to be used as a power supply.
The cylindrical secondary electrode includes a positive electrode plate coated with a positive active material, a negative electrode plate coated with a negative active material, an electrode assembly disposed between the positive electrode plate and the negative electrode plate having a separator wound in an approximately cylindrical shape for transporting lithium ions (Li-ion), a cylindrical case for receiving the electrode assembly, and an electrolyte injected into the cylindrical case for transporting lithium ions.
Generally, in such cylindrical secondary electrodes, a space exists in a center portion of the electrode assembly.
A problem associated with said space is that it provides for annealing and deformation of the electrode assembly.
Therefore, an attempt to solve this problem has been made by combining a tubular core element having a cut-off groove approximately formed along a longitudinal direction with the center space of the electrode assembly.
However, pressure may be applied to the core element by an external impact, for example, by dropping the cylindrical secondary electrode.
When the core element is subject to deformation by compression under pressure, a tip end of the cut portion stabs the electrode assembly.
In particular, when the core element is deformed or damaged, the separator of the electrode assembly is damaged. Puncture of the separator causes a short between the positive electrode plate and the negative electrode plate. Therefore, there are fatal problems in that the cylindrical secondary electrode may be destroyed or may explode.
As result, it has a serious influence on the lithium battery.